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- Glass melting furnaces
- Glass pots
- Pressing, a general descripion
- Swedish pressed glass
- Centrifuging
- Vacuum flasks




When the press came to Sweden

As we have seen, the glass press made its entrance in the 1830ies: first Reijmyre, then Skönvik, Kosta...

All seemed ready for the glass pressing to triumph.
There were experiments with different types of presses, different materials for moulds. Strömberg (Kostaglaset 1742-1916) writes about ceramic moulds, moulds made of brass and, later, iron.
But there were problems: at Kosta (Strömberg writes) one problem was that the moulds were not strong enough. In the end the solution was that the smith took care of both moulds and the actual pressing.
It took more than ten years for Kosta to produce saleable press glass.

At Skönvik they had more problems. The owner, Carl Ramström, showed some items at an industrial conference in 1838, and got lots of approval. The attending industrialists thought that "these examples are fully compatible with the imported goods, both the clarity of the metal, the colours and the quality of the patterns".
Despite this, Skönvik did not succeed: the last year they pressed any glass was in 1842. The accounts show that the total production for that year was 16 dishes, 180 bobèches (candle wax catchers) and 102 salt cellars. That quantity should have been produced in one, possibly two days.
When the glassworks was closed in 1870, the press and the press moulds were still there, forgotten since nearly 30 years.

From around 1850-60 pressed glass became more common, and several glassworks bought presses.
The moulds were often imported, but eventually even the Swedes learnt to make press moulds. One of the still remembered makers was named Johan Wilhelm Bergström from Stockholm. The reason he is remembered is that he marked his moulds with IVB inside the mould: his signature shows on all items pressed in one of his moulds.
Here in Småland we prefer to remember Stenberg's foundry and mechanical workshop in Lindås outside Emmaboda. The moulds from Stenberg often has a mark, but not where it shows on the glass.

By this time the moulds had evolved, became more complex: open-and-shut moulds had two, three, four parts, to make it possible to manufacture pieces with "strange" forms.
Below an example, probably made by Stenberg, open-and-shut mould in four parts, and the result:

saltcellar with mould
Considerable skill was needed to get a "good" product out of this mould, ie that the glass filled every cavity of the mould - the melt had to be fluid (hot) enough, but not too hot, because too hot glass tends to stick to the mould. The mould itself had to be pre-heated to the optimal temperature.


Two more examples: to the left a four-part mould for a candlestick from Stenbergs; to the right a three-part mould for a creamer – this mould is on display in the museum.

four-part mould for a candlestick
three-part mould for creamer "Hjärta"

 

The pressed products became more and more important for the economy of the glassworks.

In Teknisk tidskrift in april 1935, Edvard Strömberg, then manager at Strömbergshyttan, writes:
«
[…] At the presses the molten glass is poured into engraved iron moulds and pressed with a plunger to make the glass fill all the details of the mould. It is then stuck up on a pontil, re-heated and can be manipulated to get nearly any form. It also gets a blank surface.
Previously America alone was capable of making excellent pressed glass.
Oil-heated furnaces have made it possible also for us in Sweden to produce a very good press glass.
Earlier, for ordinary drinking glasses, it was possible to press 250 pieces per hour with a mean weight at 220 grams. Nowadays, the weight is down to 130 grams, and the speed has increased to 400 per hour, a good achievement by the presser, who has to do 5 separate motions per glass.
   »
(my translation, and my italics)

Let us, for fun, do a little math:

Let us suppose, not to exaggerate, that there were seven effective hours per day.

Let us suppose, not to understate, that the pressing team had tre workers.

7 hours x 400 glasses = 2800 "ordinary drinking glasses" per day, or 6,6 glasses per minute, or 9 seconds per glass.

If the team consisted of 3 persons, it will mean that the total salary cost per glass came to less than 30 seconds (a half-minute). Of course there are more to the production cost than salary: cost of raw materials, for melting, for machines and buildings etc – but it is easy to understand that pressed glass had become a veritable "cash crop" for the glassworks.

We can also remember, and compare, to the total 1842 production at Skönvik (95 years previous): 16 dishes, 180 bobèches and 102 salt cellars.

 

Read about the presses we show in the museum.



I found a video showing comtemporary hand pressing. They make a bowl, that can be used "as is", but it can then be flared into a dish. The dish can be swaged and can get a handle added, making it into a "candy basket".

It is obvious that the moulds are an important part of the end result. I fould another video about making moulds for pressing glass: